The present invention relates generally to the slide projector art, and more particularly concerns lap-dissolve slide projectors.
Most conventional slide projectors use a single projection optics system, so that in operation of the projector, an individual slide is successively acquired from a slide receptacle, moved into the projection optics system, where it is projected on a screen, and then returned to the slide receptacle. With single projection optics projectors, there is a time lapse between the projection of successive slides, to permit the slide just projected to be returned to the slide receptacle, before the following slide is acquired from the slide receptacle and positioned in the projection optics system. This time lapse, when the screen is blank, can be quite long, and is disruptive of the slide presentation.
A significant amount of effort has been expended in order to correct this disadvantage of conventional slide projectors. So-called lap-dissolve slide projectors have been developed specifically to eliminate the blank screen between successive slides. Typically, a lap-dissolve slide projector includes two projection optics systems which are synchronized with one or two slide receptacles. In operation, the next slide to be projected is moved into one projection optics system while the previous slide is being projected by the other optics system. Thus, when the slide being projected is to be returned to the slide receptacle, the next slide is ready to be projected, and the first slide can be dissolved into the next, by use of known shutter or mirror techniques. This results in a continuous sequence of images on the screen, eliminating the blank screen.
Such a result, however, has previously required a sophisticated mechanism for moving the slides between the slide receptacle(s) and the projection optics systems, as well as complex control mechanisms to properly sequence the various mechanical and electrical subsystems to accomplish the lap-dissolve technique.
A number of technical approaches has been used in this area. One approach uses multiple or single linear slide receptacles with two projection optics systems, in a single projector. Examples of such approaches are shown in U.S. Pat. Nos. 3,468,603 and 3,501,232. The mechanical systems which have been developed to implement these approaches have, however, proved to be too complex to be reliable or commercially practical. Further, they both require linear slide trays, which are no longer widely used.
There are relatively few lap-dissolve single projectors capable of operating with circular slide trays, even though such trays are now common in the industry. One lap-dissolve slide projector known to applicant using a circular slide tray is the subject of U.S. Pat. No. 3,689,140. The circular slide receptacle in that projector is shifted laterally to serve two projection optics systems. The mechanical structure to implement such an arrangement, however, is very complicated and hence, commercially impractical.
Another common approach uses two projectors. When two projectors are used, however, successive slides must be alternately taken from the slide receptacles of each projector, thus requiring two slide receptacles for each presentation, with the slides stored in an alternating sequence between them. This has proven to be an inconvenient storage arrangement. Additionally, the control and synchronization required to make two projectors operate as a single lap-dissolve unit results in a cumbersome combination which is often very complicated for the user to successfully operate.
In view of the above, it is a general object of the present invention to provde a multiple projection optics slide projector which overcomes one or more of the disadvantages of the prior art noted above.
It is another object of the present invention to provide such a slide projector which combines multiple projection optics systems and a single slide receptacle to accomplish a continuous slide presentation in a single projector.
It is a further object of the present invention to provide such a projector which is capable of using a circular slide receptacle.
It is an additional object of the present invention to provide such a slide projector in which one or more of the operating subsystems of the slide projector is capable of operating independently of other subsystems.
It is yet another object of the present invention to provide such a slide projector in which slides are returned to the slide receptacle in the same order as they are removed therefrom.